Sustainable recovery of critical metals from spent lithium-ion batteries using chitosan as biosorbent in citrate-sulfate media: A comprehensive isotherm, kinetic, and thermodynamic analysis

This study showcases the ability of chitosan powder to selectively adsorb Co(II), Mn(II), and Ni(II) from spent lithium-ion batteries within a sulfate-citrate medium while effectively maintaining Li in solution. Characterization via BET, FT-IR, and TGA analyses revealed that amine and hydroxyl groups are key players in adsorption. Considerably high adsorption rates for Co(II) and Ni(II), surpassing 80%, underscore chitosan's potential for robust metal ions retrieval. Notably, chitosan exhibits negligible adsorption capacity for Li, keeping it predominantly in solution, thus providing a selective separation and recovery method. Optimum parameters were determined as a dilution factor of 40, pH 4, and an adsorbent dosage of 10 g/L. While pH variations minimally affected Co(II) and Ni(II) recovery, Mn(II) removal rates increased with pH. Using the Langmuir isotherm model, adsorption capacities for Co(II) and Ni(II) were estimated at 1.86 mmol/g (or 110 mg/g) and 0.37 mmol/g (or 20 mg/g), respectively. Mn followed the Freundlich isotherm model, and its adsorption uptake was 0.02 mmol/g (1.10 mg/g) at an equilibrium concentration of 0.47 mmol/L. Kinetic studies highlighted rapid Co(II) and Ni(II) adsorption within 5 min, confirming surface reaction as the rate-limiting step, while thermodynamic analysis revealed favorable Co(II) and Ni(II) adsorption compared to unfavorable Mn(II) adsorption. Optimal desorption was achieved with 0.01 M sulfuric acid, achieving complete desorption for Co(II) and Ni(II) and over 82% for Mn(II). These findings underscore chitosan powder's potential as a sustainable and efficient green adsorbent for selective metal ions recovery in battery recycling, addressing crucial environmental and resource conservation concerns.